gcc/ada/s-rannum.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUN-TIME COMPONENTS                         --
   4 --                                                                          --
   5 --                S Y S T E M . R A N D O M _ N U M B E R S                 --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 2007-2013, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
  17 --                                                                          --
  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
  21 --                                                                          --
  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNAT was originally developed  by the GNAT team at  New York University. --
  28 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 --  Extended pseudo-random number generation
  33
  34 --  This package provides a type representing pseudo-random number generators,
  35 --  and subprograms to extract various uniform distributions of numbers
  36 --  from them. It also provides types for representing initialization values
  37 --  and snapshots of internal generator state, which permit reproducible
  38 --  pseudo-random streams.
  39
  40 --  The generator currently provided by this package has an extremely long
  41 --  period (at least 2**19937-1), and passes the Big Crush test suite, with the
  42 --  exception of the two linear complexity tests. Therefore, it is suitable
  43 --  for simulations, but should not be used as a cryptographic pseudo-random
  44 --  source without additional processing.
  45
  46 --  Note: this package is in the System hierarchy so that it can be directly
  47 --  used by other predefined packages. User access to this package is via
  48 --  the package GNAT.Random_Numbers (file g-rannum.ads), which also extends
  49 --  its capabilities. The interfaces are different so as to include in
  50 --  System.Random_Numbers only the definitions necessary to implement the
  51 --  standard random-number packages Ada.Numerics.Float_Random and
  52 --  Ada.Numerics.Discrete_Random.
  53
  54 with Interfaces;
  55
  56 package System.Random_Numbers is
  57
  58    type Generator is limited private;
  59    --  Generator encodes the current state of a random number stream, it is
  60    --  provided as input to produce the next random number, and updated so
  61    --  that it is ready to produce the next one.
  62
  63    type State is private;
  64    --  A non-limited version of a Generator's internal state
  65
  66    function Random (Gen : Generator) return Float;
  67    function Random (Gen : Generator) return Long_Float;
  68    --  Return pseudo-random numbers uniformly distributed on [0.0 .. 1.0)
  69
  70    function Random (Gen : Generator) return Interfaces.Unsigned_32;
  71    function Random (Gen : Generator) return Interfaces.Unsigned_64;
  72    --  Return pseudo-random numbers uniformly distributed on T'First .. T'Last
  73    --  for builtin integer types.
  74
  75    generic
  76       type Result_Subtype is (<>);
  77       Default_Min : Result_Subtype := Result_Subtype'Val (0);
  78    function Random_Discrete
  79      (Gen : Generator;
  80       Min : Result_Subtype := Default_Min;
  81       Max : Result_Subtype := Result_Subtype'Last) return Result_Subtype;
  82    --  Returns pseudo-random numbers uniformly distributed on Min .. Max
  83
  84    generic
  85       type Result_Subtype is digits <>;
  86    function Random_Float (Gen : Generator) return Result_Subtype;
  87    --  Returns pseudo-random numbers uniformly distributed on [0 .. 1)
  88
  89    type Initialization_Vector is
  90      array (Integer range <>) of Interfaces.Unsigned_32;
  91    --  Provides the most general initialization values for a generator (used
  92    --  in Reset).  In general, there is little point in providing more than
  93    --  a certain number of values (currently 624).
  94
  95    procedure Reset (Gen : Generator);
  96    --  Re-initialize the state of Gen from the time of day
  97
  98    procedure Reset (Gen : Generator; Initiator : Initialization_Vector);
  99    procedure Reset (Gen : Generator; Initiator : Interfaces.Integer_32);
 100    procedure Reset (Gen : Generator; Initiator : Interfaces.Unsigned_32);
 101    procedure Reset (Gen : Generator; Initiator : Integer);
 102    --  Re-initialize Gen based on the Initiator in various ways. Identical
 103    --  values of Initiator cause identical sequences of values.
 104
 105    procedure Reset (Gen : Generator; From_State : Generator);
 106    --  Causes the state of Gen to be identical to that of From_State; Gen
 107    --  and From_State will produce identical sequences of values subsequently.
 108
 109    procedure Reset (Gen : Generator; From_State : State);
 110    procedure Save  (Gen : Generator; To_State : out State);
 111    --  The sequence
 112    --     Save (Gen2, S); Reset (Gen1, S)
 113    --  has the same effect as Reset (Gen2, Gen1).
 114
 115    procedure Reset (Gen : Generator; From_Image : String);
 116    function Image (Gen : Generator) return String;
 117    --  The call
 118    --     Reset (Gen2, Image (Gen1))
 119    --  has the same effect as Reset (Gen2, Gen1);
 120
 121    Max_Image_Width : constant := 11 * 624;
 122    --  Maximum possible length of result of Image (...)
 123
 124    function Image (Of_State : State) return String;
 125    --  A String representation of Of_State. Identical to the result of
 126    --  Image (Gen), if Of_State has been set with Save (Gen, Of_State).
 127
 128    function Value (Coded_State : String) return State;
 129    --  Inverse of Image on States
 130
 131 private
 132
 133    N : constant := 624;
 134    --  The number of 32-bit integers in the shift register
 135
 136    M : constant := 397;
 137    --  Feedback distance from the current position
 138
 139    subtype State_Val is Interfaces.Unsigned_32;
 140    type State is array (0 .. N - 1) of State_Val;
 141
 142    type Writable_Access (Self : access Generator) is limited null record;
 143    --  Auxiliary type to make Generator a self-referential type
 144
 145    type Generator is limited record
 146       Writable  : Writable_Access (Generator'Access);
 147       --  This self reference allows functions to modify Generator arguments
 148
 149       S : State := (others => 0);
 150       --  The shift register, a circular buffer
 151
 152       I : Integer := N;
 153       --  Current starting position in shift register S (N means uninitialized)
 154       --  We should avoid using the identifier I here ???
 155    end record;
 156
 157 end System.Random_Numbers;